1. Field of Invention
The present invention relates to polyester fibers that contain a small amount of additives, and to a method for their production.
2. Description of the Related Art
It is known that fibers [or filaments] that contain small quantities of additives, depending on the composition of the mixture, can be processed by melt spinning, and sometimes, at the same spinning speed, can result in an increase in the elongation at break in the undrawn yarn.
EP 0,047,464 B1 teaches that polymethyl methacrylate (abbreviated as PMMA hereafter) can be used in principle to increase the elongation at break at higher spinning rates.
This document describes the use of regranulated material, mixed in molten state, consisting of polyester with the addition of polymethyl methacrylate. This procedure is the optimum kind of premixing to achieve a homogenous product. However, as evidenced in EP 0,047,464 B1, when polymethyl methacrylates with high-molecular weights are used as additives, problems arise in the spuming process (see p.5, lines 11-13).
EP 0,631,638 B1, like EP 0,047,464 B1, also describes the fact that polymethyl methacrylate has a limited capacity for spinning. EP 0,631,638 B1 describes a fiber polymer that contains from 0.1-5 wt %, relative to the fiber polymer of a 50-90% imidized polymethacrylic acid alkyl ester, essentially in the form of inclusions. A significant disadvantage of imidized polymethacrylic acid alkyl ester additives, however, is the relatively high price of the additive. The costs of the imidized polymethacrylic acid alkyl ester show that a process that requires the named additive is not economical. Furthermore, the described additive cannot be obtained on a large scale and is also dependent on the few existing manufacturers. Another disadvantage is, as described above, that the spinning safety is limited. When this material is used as an additive, there are more often fiber breakages.
The maximum molecular weight of the polymethyl methacrylate described in EP 0,047,464 B1 is 16,000 g/mol (see p. 9, Table 5). Furthermore, in this document it is mentioned that, for PMMA drop diameters in the polyester matrix of more than 1 xcexcm, the increase of elongation is no longer optimal. Otherwise, there is no further discussion of the morphology of the inclusions.
Normally, as also described in EP 0,047,464 B1 and in xe2x80x9cHP5 The Highly Economical POY Process for Polyester, Fiber Producer Conference, Greenville, 1998,xe2x80x9d such incompatible inclusions appear in the unoriented polyester free fall yarn, that means, in the unoriented molten fibers extruded from the spinneret inclusions appear in the form of balls or drops. In EP 0,047,464 B1, it is stated on p.4, lines 13-15, as well on p.5, lines 8 and 9, that the inclusions possibly (similar to a ball bearing) cause a xe2x80x9croll effectxe2x80x9d in the fiber direction that leads to a delayed deformation of the polyester.
A possible association of special forms and sizes of additive inclusions in the still unoriented polyester free fall yarn, with the special properties by respect to the end product required here and with the important spinning behavior essential for an industrially useful process, on the contrary, was not recognized.
The objective of the present invention, therefore, is to make available polymer mixtures for the production of polyester fibers that can be spun well and contain no more than 4 wt % additives, whereby the production method, due to the small additive quantity, should have a broad availability of the additive, and due to the great increase of the elongation at break, should be highly economical.
This objective is achieved by the fibers and the method according to the present invention.
In one aspect, the present invention provides fibers consisting predominantly of polyethylene terephthalate as a fiber-forming polymer, characterized in that the fibers contain 0.1-4 wt %, relative to the fiber-forming polymer, polymethyl methacrylate with a weight-averaged molecular weight of about between 20,000 and 200,000 g/mol, predominantly in the form of rod shaped inclusions, measured in a still-unoriented melt fiber free fall yam extruded from a spinneret, whereby the cross-section of the rod shaped inclusions of the polymethyl methacrylate is less than 800 nm, and whereby the spinning speed of the spinning fiber in the production of the fibers is up to 8000 m/min.
In another aspect, the present invention provides a method for the production of melt-spun fibers comprising polyethylene terephthalate as a fiber-forming polymer, through polycondensation or melting of the fiber-forming polymer forming a melt and subsequently melt spinning. The method comprises mixing 0.1-4 wt %, relative to the fiber-forming polymer, of a second polymer consisting essentially of polymethyl methacrylate with an average molecular weight of about between 20,000 and 200,000 g/mol, with of the fiber-forming polymer before the melt spinning and dispersing the second polymer in the fiberforming polymer forming unoriented melt fibers, and during the melt spinning, a spinning speed of the fibers is set at up to 8000 m/min, whereby through the inclusion in the unoriented melt fibers, extruded from a spinneret, [rod-shaped]rod shaped inclusions of the second polymer with a cross-section of less than 800 nm are obtained.